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2월, 2019의 게시물 표시

JS 5.7 task1 Filter unique array members

<HTML> <body> </body> <script> function unique(arr){ return Array.from(new Set(arr)); } let values = ["Hare", "Krishna", "Hare", "Krishna", "Krishna", "Krishna", "Hare", "Hare", ":-O" ]; //alert( unique(values) ); // Hare, Krishna, :-O alert(unique(values)); </script> </HTML>

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JS 5.6 Iterables

<HTML> <body> </body> <script> let range = { from: 1, to: 5, [Symbol.iterator]() { this.current = this.from; return this; }, next() { if (this.current <= this.to) { return { done: false, value: this.current++ }; } else { return { done: true }; } } }; let arr = Array.from(range, num => num * num); //second argument arrows each member of the object alert(arr); </script> </HTML> //itearble means an object with Symbol.iterator and next() //so that it can be used for for - of and array.from //array-like is an object, which have an index for each item //and have an member length //string has both traits of arraylike and iterable, //but normally both trait cannot stand together in one object

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JS 5.5 task 12 Filter unique array members

<HTML> <body> </body> <script> function unique(arr){ let result = []; for(let item of arr){ if (!result.includes(item)) result.push(item); } return result; } let strings = ["Hare", "Krishna", "Hare", "Krishna", "Krishna", "Krishna", "Hare", "Hare", ":-O" ]; alert( unique(strings) ); // Hare, Krishna, :-O </script> </HTML>

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JS 5.5 task 11 Get average age

<HTML> <body> </body> <script> let john = { name: "John", age: 25 }; let pete = { name: "Pete", age: 30 }; let mary = { name: "Mary", age: 29 }; let arr = [ john, pete, mary ]; function getAverageAge(arr){ return arr.reduce((sum, curr) => sum + curr.age, 0) / arr.length; } alert(getAverageAge(arr)); </script> </HTML>

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JS 5.5 task10 Shuffle an array

<HTML> <body> </body> <script> let arr = [1,2,3]; function shuffle(array){ array.sort(() => Math.random() - 0.5); //since math.random() returns a number between 0 and 1 //by - 0.5, it can be a negative or positive //and the sorting function compares //each element by that randomly generated returned value } shuffle(arr); alert(arr); shuffle(arr); alert(arr); shuffle(arr); alert(arr); </script> </HTML>

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JS 5.5 task9 Sort objects

<HTML> <body> </body> <script> let john = { name: "John", age: 25 }; let pete = { name: "Pete", age: 30 }; let mary = { name: "Mary", age: 28 }; let arr = [ john, pete, mary ]; function sortByName(arr){ arr.sort((a,b) => { if(a.age > b.age) return 1; if(a.age == b.age) return 0; if(a.age < b.age) return -1; }); } sortByName(arr); alert(arr[0].name); // John alert(arr[2].name); // Pete </script> </HTML>

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JS 5.5 task8 Map to objects

<HTML> <body> </body> <script> let john = { name: "John", surname: "Smith", id: 1 }; let pete = { name: "Pete", surname: "Hunt", id: 2 }; let mary = { name: "Mary", surname: "Key", id: 3 }; let users = [ john, pete, mary ]; let usersMapped = users.map(function(item){ let obj = { fullName : item.name + " " + item.surname, id : item.id }; return obj; }); alert( usersMapped[0].id ) // 1 alert( usersMapped[0].fullName ) // John Smith </script> </HTML>

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JS 5.5 task7 Map to names

<HTML> <body> </body> <script> let john = { name: "John", age: 25 }; let pete = { name: "Pete", age: 30 }; let mary = { name: "Mary", age: 28 }; let users = [ john, pete, mary ]; let names = users.map((item => { return item.name; })) alert(names); </script> </HTML>

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